Sounds to me like picopsu itself might be defective. Have you tested the pico on an atx motherboard yet? Or just Amigas?
I use to use a 80 watt pico on my A1200 without issue. It has a FastATA interface with 32 GB flash storage and Blizzard 1260 accelerator. Worked fine.
Also as an FYI my setup only drew about 21 watts from the wall.